Would leave oil in rather than drain....old oil won't rust parts...will keep them from rusting: however, old oil will become acidic, eat away etch bearings and surfaces, people change oil every 7000 miles or 3 months, which ever is first, because of the acid formed in the oil from blow by gasoline, gone by the piston rings...extra 3 months not best practice, but would not ever leave it empty...that would be the worst thing ever to do...